Density functional theory study of transition-metal compounds containing metal-metal bonds. 2. Molecular structures and vibrational spectra of dinuclear tetracarboxylate compounds of molybdenum and rhodium

Vibrational spectra have been calculated for the first time for dinuclear transition-metal compounds containing metal-metal bonds. The calculations were carried out by employing different forms of density functional theory (DFT) and basis functions of different sizes at fully optimized molecular geometry. The calculated frequencies essentially reproduced fundamentals observed in experimental infrared and Raman spectra. It is shown that DFT frequency calculations can be a very important and valuable tool to assist in analyzing and assigning measured infrared and Raman spectra and to predict vibrational frequencies for large transition-metal compounds with metal-metal bonds. The molecules included in this study were M-2(O2CH)(4) (M = Mo, Rh), Rh-2(O2CH)(4)(H2O)(2), and M-2(O2CCH3)(4) (M = Mo, Rh). Significant differences are found between the formate and acetate molecules.